Short wave converter



Aug. 31, 1937.

Filed Dec. 28, 1935 ATTORNEY IN VENTOR Hrus 711a Patented Aug. 31, 1937 UNITED STATES SHORT WAVE CONVERTER Leo J. Hruska, Merchantville, N. J., assigncr'to Radio Corporation of America, a corporation of Delaware Application December 28, 1935, Serial No. 56,409 3 Claims. (01. 25o 20) My invention relates to radio receivers. Specifically my invention relates to a radio receiver in which a single thermionic tube is used as an oscillating detector, a super-regenerative detec- 5 tor, and a modulator-converter which supplies modulated intermediate frequency currents for superheterodyne reception.

I am aware of the circuits employed for regenerative, super-regenerative, and superheterodyne reception of radio frequency signals. I propose to combine several separate functions in a single thermionic tube. In the preferred form a single triode may be used. My invention not only simplifies the circuits, and uses a single tube,

but it also permits single control operation with a single variable element.

One of the objects of my invention is in the design of a single triode tube as an oscillating detector, a super-regenerative detector, and a modulator-converter.

Another object of my invention is to provide a super-regenerative-superheterodyne receiver with a single tuning element.

A further object is the design of a very sensi- 95 tive ultra short wave receiver which converts and modulates the ultra short waves to waves of a different length.

Additional objects will be apparent from the accompanying specification, drawing, and claims.

Reference to the drawing, which is an illustration of one embodiment of the circuits employed in my invention, is the best means of understanding the invention. In this drawing, an antenna l is coupled through a capacitor 3 to an inductor 5. 35 The junction between thecapacitor 3 and inductor 5 is connected to the grid 1 of a thermionic tube 9. The cathode l l of the thermionic tube 9 is grounded. The cathode may be of the filament,

or unipotential type. Batteries for heating this 4 cathode, or the cathodes of other tubes about to be described, have been omitted for simplicity.

Any suitable current source may be used, as is well understood by those skilled in the art.

The anode l3 of tube 9 is connected to one terminal of an inductor [5. The other terminal of this inductor i5 is connected through an inductor ii to the positive terminal of a B battery I9, or the like. The negative terminal of the B battery is grounded. The battery may be bypassed by a capacitor 2 I. A variable capacitor 23 is con nected between the grid 1 and the anode l3. A

second capacitor 25, which may be variable, is

connected from the lower terminal of the inductor 5 to the lower terminal of the inductor l5. This 55 capacity acts as a bypass for ultra high frequency currents. It may be used to tune or control feedback.

Neglecting for the moment the direct current path from grid 7 to ground, with properly chosen values of inductance and capacitance, the tube 5 and circuits thus described will operate as an ultra high frequency oscillator. By way of example, ultra high frequencies are from 30 megacycles to 100 megacycles and upward. The inductor I5 is chosen so that it will offer aninductive 10 reactance to currents of the received frequency to insure a strong regenerative feedback. The single variable tuning capacitor 23 acts as the tuning element which controls the frequency of the received signal representing currents and the 15 frequency of the circuits as a local oscillating detector.

I shall now describe the circuits for the quench frequency oscillator. The quench frequency is the low frequency potential which is applied to the grid of a regenerative detector to obtain super-regenerative operation. Super-regenerative operation is well known to those skilled in the art. A recent discussion of this type of op eration is found in the Proceedings of the Instia tute of Radio Engineers, vol. 23, Number 8, page 8410f August, 1935.

The quench frequency oscillator circuits are from the grid 1 through inductor 5, through a radio frequency choke 2! to a grid resistor 29- grid capacitor 3| combination. The lower terminal of the grid resistor-grid capacitor combination is connected to the upper terminal of a tank circuit 33. The tank circuit 33 is composed of a semi-variable, capacitor 35 and an inductor 31. The lower terminal of the tank circuit is grounded.

The anode circuit is composed of the inductors I5 and i1, and capacitor 2|. The inductor H is mutually coupled to the inductor 37 as indicated by mutual inductive coupling M. Although I have illustrated the coupling as magnetic, any type of regenerative feedback may be employed.

Having thus briefly described the quench oscillator circuits, their operation and adjustment will be set forth. I prefer to first short circuit the ultra high frequency inductors 5 and I5. The coupling between the anode circuit inductor I! and the grid circuit inductor 3'! is adjusted to a value which causes local oscillations. The semivariable capacitor 35 of the tank circuit is adjusted until the desiredquench frequency oscillations are produced. The frequency, which I prefer, is that of a cleared channel just below the present broadcast band; for example, 500 kilocoupled as illustrated, but, if desired, inductive coupling may be employed.

The radio frequency choke 21 and bypass capacitor 25 form a net work which freely passes currents of ultra high frequency between inductor and inductor l5 and prevents the ultra high frequency currents from passing to the quench frequency circuits. The inductors 5 and H: which offer effective inductive reaction at the ultra high 1 frequencies, offer very low and negligible reactance at the lower or quenching frequency. Likewise the radio frequency choke 2'! and bypass capacitor 25 offer very small or negligible reactance to the quench frequencies.

Although I do not wish to be limited to any precise theory of operation, I believe the operation is as follows; The received signal representing currents are impressed on the grid electrode of the triode. These incoming currents are detected by the ultra high frequency oscillating detector. The usual frequencies resulting from demodulation are present. t v The detector is also being supplied with currents of the quench frequency. These currents serve two purposes:' First, the quench currents provide the well known super-regeneration operation and thereby greatly increase the sensitivity of the detector. Second, the modulation component of the received signal isimpressed on the quench frequency currents, thereby modulating these currents.

In any event a modulated carrier current oscillating at the quench frequency appears across the quench frequency anode inductor ll. These modulated carrier currents may be impressed on the input of an amplifier 39 through a small coupling capacitor ll. The input to the amplifier 39". s preferably tuned to the quench frequency by a, tank circuit 43. The output of the amplifier is likewise tuned by a tank circuit 45. The output tank circuit 35 is coupled to a resonant circuit 41. Across this resonant circuit is connected a suitable detector 49.

-The detector 49 demodulates the modulated carrier frequency currents which have been amit is possible to operate at a harmonic of the quenching frequency. In a similar manner, I have fixed the intermediate frequency and operated the quench oscillator at a sub-harmonic thereof. Other modifications within the scope of my invention will occur to those skilled in the art. The foregoing specification is by way of example and not a limitation on my invention, which only limited as required by the prior art and appended claims.

I claim as my invention:

1. A radio receiving system comprising a thermionic tube having grid, cathode, and anode electrodes,-..a first pair of circuits effectively connected to said thermionic tube for generating and detecting oscillatory currents of ultra high frequency, means for tuning said circuits over a range of ultra high frequencies, a second pair of generating currents of a substantially lower fre quency connected to said oscillating detector. means for bypassing currents of said ultra high frequency around said lower frequency circuits, means offering high reactance to said ultra high frequency currents and low reactance to said low frequency currents connected in said high frequency circuits, means whereby said lowv fre,-.

quency currents are applied to said oscillating.

detector to quench said ultra high frequency currents, and means for detecting the resulting modulation currents.

3. In an apparatus of the character described, a pair of oscillatory circuits, one of said pair of oscillatory circuits tunable over a range of ultra high frequencies, the other of said pair tuned to a single frequency substantially lower than said ultra high frequencies, a single triocle tube effectively connected to said circuits, means for. gen erating oscillatory currents within said tube and circuits of said ultra high and relatively low frequencies, means for preventing said circuits from interacting on each other and for insuring the combining of currents of each mentioned frequency 'withinsaid tube, means for impressing modulated signal frequency currents on .saidoscillating detector whereby a resultant modulated carrier of a different frequency is generated by said-tube, and means for detecting said resultant modulated carrier.

LEO J. HRUSKA. 

